In general, this invention relates to a color video printer for producing a color photographic copy from a color video signal. More particularly, this invention relates to a color video printer which has a color viewer for viewing a color video image before printing to permit evaluation of the image and, where desirable, preprinting adjustments to the characteristics of the image.
In producing a color copy from a color video signal, it is often desirable to evaluate the image so that any adjustments to the characteristics of the image may be made before copying. Although various video image copying devices have been proposed, these devices have generally been complex, expensive and difficult to operate. In many of these devices, the operator is provided with a viewer for viewing the video image prior to copying. One technique for producing a copy of a color video signal is to photograph the face of a color television with a color still camera. Although the television controls may be adjusted prior to photographing in order to adjust the video image to one's preference, this technique is disadvantageous in requiring the use of an expensive color television or video monitor to make a copy. Additionally, poor copy quality may result due to the difficulties (1) in synchronizing the shutter speed of the still camera with the frame rate of the video signal and (2) in positioning the camera relative to the monitor face to make the photographic image coincide with the monitor image.
In U.S. Pat. No. 4,468,693, entitled VIDEO PRINTING APPARATUS, by S. Fujita et al, issued Aug. 28, 1984, there is disclosed a complex and expensive video printing apparatus using a monochrome video monitor for producing a color print by filtering the monochrome images with stationary red, green and blue filters to produce sequential color images to which photographic film is exposed. The video image may be viewed on a separate color monitor prior to printing. This viewing technique is expensive and complex in the use of a color monitor solely for viewing and, therefore, is not readily applicable to a low cost video printer. The latter patent also discloses (FIG. 26) a monochrome CRT used with two stationary color filter wheels, one used in producing a color print and the other used in a shading correction circuit, but not in a viewing system. In U.S. Pat. No. 4,339,769 entitled PHOTOGRAPHY APPARATUS FOR TELEVISION PICTURE, by T. Fujita et al, issued July 13, 1982, there is disclosed apparatus for making a photographic print from a color video signal that includes a monochrome video monitor, a stationary color filter wheel and a camera. A waveform monitor is provided for separately viewing red, green, blue and luminance fields. In addition, viewing ports are provided to view the monochrome printing monitor in advance of the stationary color filter wheel. The latter apparatus is disadvantageous in the use of an expensive dedicated viewing monitor and in permitting direct viewing of only the monochrome image and not a color optical image produced by the printing monochrome CRT.
Although it has been proposed to use a monochrome monitor with a color filter wheel synchronized with the incoming video signal in order to view a video image before copying, such monitors have been used separately from the copying operation. Thus, in U.S. Pat. Nos. 4,231,061 and 2,995,619, separate diazo printing tubes are used for the copying operation so that the image produced by a monochrome tube and color filter wheel is not the image used to expose the copying material. A similar difficulty arises in the video color negative analyzers disclosed in U.S. Pat. Nos. 2,295,628 and 3,644,664 in which a slide or negative is scanned by means of a monochrome cathode ray tube (or flying spot scanner) and color filter wheel. The resulting video signal is applied to a similar monochrome imaging device and color filter wheel. In the latter patent, separate scanning and viewing assemblies are disclosed while in the former patent, the same monochrome CRT is used with synchronized scanning and viewing color filter wheels. However, in both patents copying of the negative is effected in a separate printing device.
Thus, there exists a need for a simple, inexpensive and easy to use viewer for a color video printer which obviates such difficulties.